[KartikP]

What changes

Use the same configuration and unit coordinates across model extraction, recording, interventions, and sessions.

• Normalize extraction registrations once; dispatch all modalities through the same extractor mapping.
• Keep layer, unit, and modality routing together in region selectors. Preserve composite and external selectors when mappings are read back or updated.
• Give selections an explicit axis and optional shape check, so localization, recording, and ablation identify the same units.
• Interpret raw layer names consistently for single and multiple recording targets.
• Put optional session configuration on the common session contract. Use InMemorySession for fixed stimuli, behavioral inputs, and assembly collection; retain specialized adapters for their distinct behavior.

Companion: unified #29. Merge core first. Core CI uses the coordinated unified implementation at ce340ef852c574ff4fec55377411e9ecea09347f, with the candidate core revision supplied by the workflow.

Compatibility

Simple region mappings still return layer strings. Composite or routed entries now return their full selector instead of losing information. Existing extraction registration forms and session helpers remain accepted. Unified documents its session-factory adjustment separately.

Validation

• Core required offline profile: 781 passed, no skips.
• Coordinated four-repository profiles: 2,379 passed; 43 documented optional skips, none unexpected.
• Eight core files pass type checks; all 15 offline notebooks pass with installed candidate packages.
• Broader core suite: 861 passed, with the same 8 failures and 7 setup errors as the base (842 passed), in plugin, Conda, path, and external-service checks.

Validation uses existing CPU dependencies; it does not establish fresh-install or GPU qualification.